This application claims priority on Finnish Application No. 20010462, Filed Dec. 4, 2001, the disclosure of which is incorporated by reference herein.
Not applicable.
The present invention relates to a rod cradle, with the help of which coating mixture is applied onto web material. The invention can be used, for example, in the coating of paper using the film transfer technique.
Paper can be coated using the film transfer technique, in which a coating mixture, such as a coating paste, is spread as a film onto a rotating roll and then transferred in a roll nip to the paper web to be coated. The mixture can be spread to the roll with the help of a rotatable circular film rod, which is located against the roll and parallel to the axle of the rod. From the roll nip between the film rod and the roll, the mixture is transferred as a film to the surface of the roll. The apparatus also comprises a blocking rod to be pressed against the roll, preventing the mixture from flowing downwards. The rods have been placed into rod cradles that have been connected so that a pressurized feed chamber is formed between them. The rod cradle tightly surrounds the rod from the back. The ends of the chamber are provided with edge gaskets that prevent the mixture from flowing away from the edges.
The rod cradle is generally made of suitably flexible material, such as polyurethane plastic. In this way the rod can be pressed evenly and flexibly against the surface of the roll with the help of the cradle. The cradle usually comprises a narrower base section provided with a projection. The cradle is attached to the cradle holder from the base section. An eccentric locking is generally used in fastening the cradle.
It is important in the fastening of the rod cradle that, on the one hand, the cradle can be reliably kept in the holder and, on the other hand, the fastening should be so loose that the cradle can move in the lateral direction. The mobility in the lateral direction is important due to the thermal expansion caused by the possible temperature differences between the beam and the cradle. However, if the fastening is too loose, coating mixture can leak around the base of the cradle. The leak is harmful especially in a coating apparatus without return circulation, because the roll can contain uncoated areas at the places of the leakage. For repairing the leakage, feed has to be increased so that pressure increases in the chamber and it may be necessary to increase the pressure of the blocking rod and the film rod. The leakage also causes loss and environmental contamination. In addition, the leaked coating mixture can dry to the holder and make the detachment of the cradle and the operation of the fastening mechanism more difficult. Too tight a locking of the cradle again causes profile problems in the film, as the thermal expansion of the cradle has been prevented.
The space available for the base section of the cradle is dependent on the tolerances of several parts and also on the measuring accuracy of the cradle and on the contamination of the holder. Thus, it is even possible for the optimal tightness of the fastening to easily change during the run.
In accordance with the invention, a gasket is located between the cradle and its holder, preventing the coating mixture from getting out of the chamber along this route. Because of the gasket, the fastening between the cradle and the holder can be sufficiently loose so that mobility caused by thermal expansion is possible.
The gasket can be fastened either to the cradle or to the holder, preferably to the cradle. As the gasket is located in the cradle, it is always easily changed together with the cradle.
The gasket can be fastened especially with the help of a fastening groove. The groove fastening is reliable so that the gasket does not easily become detached, for example, upon washing. However, the gasket can also be fastened, for example, by gluing.
The gasket can be for example a tube or tape gasket, especially a tube gasket. When required, pressure medium, such as air, can be directed to the tube for adjusting the sealing power. The gasket can also be a lip gasket of, for example, I, T, Y, V, U, D or P shape. The sealing material can especially be a suitable elastomer, such as silicone, nitrile or ethylene propylene diene rubber, or spring steel.
The rod attached to the cradle can be rotatable.
The cradle can be used both as a film rod cradle and a blocking rod cradle. A spreading device can have both a film rod cradle and a blocking rod cradle. Instead of a blocking rod, the device can have a blocking blade with or without a hole.
The invention can be applied especially in spreading apparatuses without return circulation, but it is also useful in traditional apparatuses provided with return circulation.
Some embodiments of the invention are next explained in more detail.